<!DOCTYPE html>
<html>
<head>
</head>

<body>
<canvas id="canvas0"></canvas>

<script>
  var canvas0=document.getElementById("canvas0");
  var ctx=canvas0.getContext("2d");
  canvas0.addEventListener("DOMAttrModified",
                                           function(event) {
                                             canvas0.toBlob(function(){},"image/jpeg",1);
                                           }, true); 
  canvas0.setAttribute("height",470)
</script>

</body>
</html>
